Chemical and biological studies of medicinal plants used by the Yaegl Aboriginal community of Australia

Abstract

"A thesis submitted as partial fulfilment of the requirements for the degree of Doctor of Philosophy, Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, Australia, 2013".Bibliography: pages 193-210.Chapter 1. Introduction -- Chapter 2. Selection of plants and methods for screening and isolation of bioactive compounds -- Chapter 3. Chemical and biological studies on Lophostemon suaveolens -- Chapter 4. Chemical and biological studies on Alphitonia excelsa -- Chapter 5. Ethical engagement with community and capacity strengthening -- Chapter 6. Conclusion and future directions."This PhD study was based on the ethnomedicinal knowledge of the Yaegl Aboriginal community of northern NSW, Australia. It follows previous investigations of the Indigenous Bioresources Research Group (IBRG) on first-hand documentation of and preliminary screening of some medicinal plants used by the Yaegl community for treatment of wounds, sores and skin infections. The overall aim of this project was to isolate and indentify bioactive components from two medicinal plants of the Yaegl community. Two Indigenous Australian medicinal plants, Lophostemon suaveolens and Alphitonia excelsa were selected for detailed chemical and biological studies. This selection was on the basis of a literature review on the Yaegl medicinal plants documented by the IBRG for the treatment of wounds, sores and skin infections, preliminary screening results of previous IBRG researchers, and specific Yaegl community requests. Antimicrobial activity (disc diffusion, MTT microdilution and TLC bioautography assays), anti-inflammatory activity (NO, TNF-α, PGE2 and COX inhibitory assays) and antioxidant activity (ORAC assay) of these two plants were evaluated. Leaves of L. suaveolens were extracted sequentially with n-hexane, DCM, EtOAc and MeOH. Significant antimicrobial activity was observed with the n-hexane and DCM extracts with IC90 <50 μg/mL against antibiotic sensitive and resistant strains of Staphylococcus aureus (MRSA and MDRSA) and Streptococcus pyogenes in the MTT microdilution assay. Both extracts also showed significant NO inhibitory activity in RAW264 cells with IC50 43.9 μg/mL and 4.6 μg/mL, respectively, for the n-hexane and DCM extracts. These extracts (n-hexane and DCM) did not show TNF-α or PGE2 inhibitory activity. GC-MS analysis of the oily n-hexane extract identified 16 components including the well known bioactive compounds aromadendrene (15.47%), spathulenol (12.46%), globulol (4.47%), epiglobulol (2.69%), phytol (2.84%), β-caryophyllene (2.53%) and α-humulene (1.52%). These compounds were reported for having antimicrobial (aromadendrene, spathulenol, globulol, β-caryophyllene, α-humulene and phytol), anti-inflammatory (β-caryophyllene) and cytotoxic (β-caryophyllene, spathulenol and α-humulene) properties. Further fractionation of the DCM extract by normal plase silica gel column chromatography yielded five major bioactive fractions that showed good antimicrobial (IC90 <50-1000 μg/mL range against Streptococcus pyogenes and methicillin sensitive and resistant strains of Staphylococcus. aureus), NO inhibitory (IC50 <12 μg/mL), PGE2 inhibitory (<20 μg/mL) and modest antioxidant (1000-2700 μM TE/g) activities. Further bioassay guided studies on these active fractions using different chromatographic procedures led to the isolation of betulinic acid and eucalyptin from the n-hexane and DCM extracts. Eucalyptin has been previously reported to have antimicrobial properties and betulinic acid is a well known anti-inflammatory compound. This is the first report of bioassay studies and isolation of bioactive compounds from L. suaveolens. Leaves of A. excelsa were extracted sequentially with n-hexane, DCM, EtOAc and MeOH. They were also extracted with water to mimic some preparation practices of the Yaegl community. The EtOAc extract showed promising antimicrobial activity (IC90 <50 μg/mL against S. pyogenes and IC90 500-1000 μg/mL against antibiotic sensitive and resistant strains of S. aureus) in the MTT microdilution assay. The EtOAc extract also showed potent nitric oxide (NO) inhibition (IC50 10.7 μg/mL) and promising antioxidant (3.70x10³ μM TE/g) activities. The MeOH extract of A. excelsa displayed moderate levels of antimicrobial (IC90 1000 and 62.5 μg/mL against S. aureus and S. pyogenes, respectively, in MTT microdilution assay) and anti-inflammatory (IC50 30.5 μg/mL in NO inhibition assay) activities. The water extract showed good anti-inflammatory activity in the COX inhibitory assay and modest antioxidant activity in the ORAC assay. Further bioassay guided isolation of the EtOAc extract led to the isolation of two bioactive flavonoids, kaempferol and quercetin. Both isolated compounds showed antimicrobial activity (IC90 =<62.5 μg/mL against S. pyogenes, sensitive and resistant strains of S. aureus) in the MTT microdilution assay. This is the first report of isolation of these two compounds from A. excelsa. Nurturing and sustaining a strong relationship with the Yaegl Indigenous people and providing capacity strengthening opportunities for the community was an essential part of this research. This is aligned with the best ethical practices essential for working with Indigenous people on their knowledge systems. For this PhD study, this included participation in meetings and workshops with the Yaegl community members; presenting and providing feedback on the research work and inviting feedback by the community to guide the research; and organising and participating in an education program with the local youth to enhance educational outcomes, as requested by the Yaegl community.Mode of access: World Wide Web.1 online resource (xix, 235 pages) illustrations (some coloured), maps (coloured